What 3rd party plug-ins do you have installed?
Did you install them all via installers, said to be Photoshop CS6-compatible by their makers?
Or did you copy them or link to them in another place on your drive by the Extra plug-ins folder configuration?
If none of these things apply, trying resetting your preferences by pressing Control - Shift - Alt immediately after cold-starting Photoshop. If you're quick enough to get the keys down it will prompt you to confirm removal of your current preferences, which will yield a reset to defaults.
Thanks for the reply Noel ,tried a reset to default settings as suggested no luck .As for plug ins all the usual suspects Topaz ,Nik software, Onone all which have been on for quite a while with no problem. I have just put an alien skin plugin on, could that be the cause?.